Recording sound photographically



Patented Oct. 5, 1937 Richard Schmidt and Alfred Kiister, in

Anhalt, Germany, assignors to I. G. Fan-benindustrle Aktiengcsellschaft, Frankfort-on-the- Germany No Application January 28, 1934, Serial No. 708,498. In Germany January 28, 1933 8 Claims. (01. 27H6) Our present invention relates to photographic sound recording.

One of its objects is to provide a process of producing a photographic sound record accord- 5 ing to the reversal method. Further objects will be seen from the detailed specification following hereafter.

In developing by the reversal method a film on which sounds have been photographically 10 recorded by projecting on the film an image of a source of light modulated in accordance with sounds a sound track is obtained which yields a very bad rendition of frequencies. This is particularly so in the case of a sound track recorded 15 according to the variable area method and is probably caused by the fact that for obtaining a minimum of fog in the reversed film the first exposure must be extraordinarily intense. This is clear when considering that in a section of film 20 in which after reversal there shall remain only the blackening caused by the minimum fog, the emulsion layer must be blackened throughout its thickness in the first exposure and the firstdevelopment, so that the silver -is completely removed 25 from this section in the bleaching operation. In

the reversal processes usual in the making of cine.

matographic pictures, the lowest possible blackening, after reversah'is obtained only with blackehings of between 2.5 and 3 density units, meas- 3 ured after the first development. The density D is calculated from the formula:

incident light transmitted light 35 Considering the extraordinarily large amounts .of light to which the layer, for obtaining so intense a blackening mus'tbe exposed, it is evident that the reproduction of high frequencies is heavily impaired owing to over-radiation.

4 According to this invention the rendering of frequencies of sound records produced on film to be developed by the reversal method is greatly improved by using a film having means for preventing or minimizing the formation of halation 4 eifects. The halation efi'ect produced by diilusion may practically beavoided by using, for instance, a light-sensitive material provided with a particularly fine-grained silver halide emulsion layer or with a silver halide emulsion layer which 60 contains a filter dye or the like or with both such layers. "Suitable dyes for the purpose are, for

- instance, ,Tartrazine, Orange I (Schultz, Farbstofltabellen, 6th edition, Vol. I, No. 144), Pinacyanol; furthermore, dyes which are simultaneously sensitizers, for instance, a selenocarbo- 5' cyanine or a naphthothiocarbocyanine or an unsymmetrical thioselenocarbocyanine substi tuted at the trimethenyl chain by ethyl.

The rendering of the frequencies may further be improved by preventing the production of 10 halation eilects caused by reflection, by means of an anti-halation'layer. The anti-halation layer may be arranged as a backing layer or as an intermediate layerbetween the emulsion layer and the support; it may be a layer of finely subdivided glassmakers soap or it may be made of a suitable red dye which is soluble in the photographic treating baths, for instance, Aurine (Schultz, Farbstofltabellen, 6th edition, Vol. I, No. 555), or

it may be a layer of colloidal silver. If the lightsensitive material is exposed through the support, the anti-halation layer is applied on the light-sensitive layer.

The process of recording sounds on film to be developed bythe reversal method as described may be used for the production of films bearing besides a sound record also a picture "record.

What we claim is:

1. A process of manufacturing a sound record which comprises projecting a slot-like picture of a source of light modulated in accordance with sounds on a'reversal film while preventing halation efiects by reflection as well as difiusion, ex-

posing said reversal film so-that the parts of the film having received the longest exposure show after the first development a blackening of 2.5 to 3, developing said film, bleaching said developed film, exposing said film a secondctime, and developing said film a second time.

2. A process of manufacturing a sound record 40 which comprises projecting a slot-like picture of a source of light modulated in accordance with sounds on a reversal film bearing a fine-grained silver halide emulsion layer and an anti-halation layer dyed'with a dye soluble in the photographic treating baths, exposing said reversal film so that the parts of the film having received the longest exposure show after the first development .a blackening of 2.5 to 3, developing said film,

bleaching said developed film, exposing said filmso a a second time, and developing said film a second time.

3. A process of manufacturing a sound record which comprises projecting a slot-like picture of a source of light modulated in accordance with sounds on a reversal film provided with a filter dye preventing halation by diffusion and soluble in the photographic treating baths, and

an'anti-halation layer dyed with a dye soluble 

